History, Groups, and Info on the Periodic Table9/4/08

Part I: History of the PT• by 1860, more than 60 elements had been discovered (this is

almost 40 years before the Thomson model debuted).

• however, there was no uniform way established to measure atomic masses accurately, and therefore…

• chemical formulas were almost impossible to determine correctly.

• September 1860—Germany—group of chemists assembled to settle the issue of atomic mass (and other misunderstood atomic matters).• Cannizarro, Stanislao—presented accurate

method to measure atomic mass.

• Mendeleev, Dimitri—1869—used this new information to organize and arrange the elements (this is the 1st time it was attempted).

Cannizarro

• Mendeleev, Dimitri—1869—used this new information to organize and arrange the elements (this is the 1st time it was attempted).

• arranged the elements according to known properties and in order of increasing atomic weight

• he noticed a trend—by arranging elements in 6 rows, he noticed a repeat in their properties down each column (this is known as a periodic pattern).

Mendeleev

• he noticed a trend—by arranging elements in 6 rows, he noticed a repeat in their properties down each column (this is known as a periodic pattern).

• some elements had not yet been discovered, so he left spaces for them. He also predicted what properties these undiscovered elements would have.

• later on, the elements that would fit in those spaces were discovered, and their properties matched what he predicted.

• some discrepancies existed (iodine and tellurium).

• Moseley, Henry—1911—used Mendeleev’s PT to write the periodic law.

• periodic law: the physical and chemical properties of the elements are periodic functions of their

atomic numbers.• he arranged elements in order of atomic number, not weight.• Today’s PT is arranged by atomic number, thanks to Moseley.

Part II: Groups of the PT• on the PT, a horizontal row is called a period, and a vertical

column is a group.• sometimes, other parts (other than single columns) are

referred to as “groups.”• each group of the PT shares similar chemical and physical

properties. • intensity of these properties tends to increase down a

group.

Moseley

• each group of the PT shares similar chemical and physical properties.

H

Family

Period

• alkali metals = very reactive with most substances, especially water and air. Form oxides easily, have a silvery appearance. Soft in pure form —can be cut with knife. Stored under kerosene or mineral oil.

(e- config ends in s1)

HNa

Na reacting with H2O

• alkaline-earth metals = not as reactive as alkali metals. Harder, denser, and stronger. Have higher melting points. Form alkaline solutions when dissolved in water (pH >7). (e- config ends in s2)

H

Mg

Ba in oil

• transition metals = good conductors of electricity and heat. High luster. Less reactive than first 2 groups. Some exist as free elements (Pd, Pt, Au, Cu, Ag). Ductile (can be pulled into a wire), malleable (can be hammered, rolled into thin sheets). (e- config ends in d1-10)

H

Mn

Cu

• The p-block is divided into three types of elements:• p-block metals: elements below the metalloid line. Very

similar to the s- and d-block metals.• nonmetals: elements above the metalloid line. Are brittle,

non-conductors, some gases (includes H).

H Ga

P

• metalloids: on the metalloid line = B, Si, Ge, As, Sb, Te. Have properties of metals and nonmetals. Semiconductors.

• halogens = highly reactive nonmetals. React with metals to form salts. Used in halogen lighting. (e- config ends in s2p5)

H

Si

I

• noble gases: unreactive. Very rarely form compounds with any element. Used in neon signs. (e- config ends in s2p6)

• lanthanides = top row of f-block. Very similar in chemical properties. Mostly natural. (e- config ends in 6s24f1-14).

• actinides = bottom row of f-block. Very similar in chemical properties. Mostly synthetic. Some used in nuclear chemistry.

(e-config. ends in 7s25f1-14).HXe

Nd

U